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#include <bits/stdc++.h>
#define boost                                                                  \
  ios_base::sync_with_stdio(0);                                                \
  cin.tie(0);                                                                  \
  cout.tie(0)
#define debug(x) cerr << #x << " " << x << endl
#define ll long long
#define int long long
#define st first
#define nd second
using namespace std;

int cities[500013];
int n, result = INT_MAX;

int calculate_result(int mask) {
  int sum = cities[1];
  int res = 0;

  for (int i = 1, bit = (1 << (n - 2)); i < n; i++, bit >>= 1) {
    if (mask & bit) {
      res++;
      sum += cities[i + 1];
    } else {
      if (sum < 0) {
        return INT_MAX;
      }
      sum = cities[i + 1];
    }
  }
  return sum < 0 ? INT_MAX : res;
}

int32_t main() {
  boost;
  cin >> n;

  for (int i = 1; i <= n; i++) {
    cin >> cities[i];
  }

  for (int i = 0; i < (1 << (n - 1)); i++) {
    result = min(result, calculate_result(i));
    // result = min(result, calculate_result(i));
  }

  result = result == INT_MAX ? -1 : result;
  cout << result << endl;
}